1. Field of the Invention
This invention relates to a method and apparatus for adjusting the looper operation locus of a sewing machine. More particularly, the present invention provides an overlocking sewing machine using upper and lower loopers with a means wherein, a looper guide, holding and guiding the upper looper, is engaged and held so as to be movable in a direction intersecting the guiding direction of the looper with a rotary carriage rotatably set with a pivot. Even more particularly, the present invention concerns a looper operation locus for sewing thin things having only the upper dead center shifted from a position near a needle plate to a higher position by deviating and moving only the looper guide without moving the pivot of the rotary carriage, and while keeping the displacement of the initial position of the upper looper as small as possible.
2. Prior Art
Generally the upper looper of an overlocking sewing machine makes on overedge motion from below its needle plate to above the needle plate. This motion locus must be properly selected depending on the thickness of the texture to be sewn.
When sewing a thick texture, the tip of the upper looper must be positioned away above the upper surface of the needle plate. However, when sewing a thin texture, the tip of the upper looper must be positioned near above the upper surface of the needle plate. This adjustment is made by a careful investigation of the geometrical formation in the motion mechanism of the looper. But it is very difficult to determine a new proper looper motion locus.
As a result there exists a need for a structure for obtaining some favorable looper operation loci.
To this end the present invention is directed to means and methods for changing the height of the upper dead center while keeping the displacement of the initial position, i.e., the lower dead center of the upper looper, as small as possible so that the misconnections of the thread produced when the upper looper makes a relay with the lower looper at the lower dead center may be reduced.